While the fuel pump is also one factor that can cause your battery to drain, it does so indirectly. In fuel injected systems, the Fuel Pump is usually powered by electricity and operates when the ignition is turned on, but not started. A healthy Fuel Pump only draws a bit of power, but when the pump no longer returns to idle pressure or fails to shut down properly, it can start constantly drawing full power with the engine off. One can drain the battery leaving it on with a parasitic draw over time.
The fuel pump is the device that most often goes bad and in many cases needs constant power to remain operational. For instance, if the electric Fuel Pump in a normal operation pulls 3-5 amps during engine running, therefore a bad one might still be drawing similar currents even after the vehicle is off. This draws a fair amount of power out over several hours or an entire night and left unattended, can drain a car battery that is fully charged to the point where you will not be able to start the vehicle tomorrow.
One of the more typical signs that there is a parasitic drain from something like the Fuel Pump effecting your vehicle will be finding a dead battery after the vehicle has sat for an extended period. Fuel Pump: If this occurs regularly and there is nothing obviously wrong with the battery or alternator, have your fuel pump checked as it may be an issue. A current draw test can be conducted to determine if the Fuel Pump is consuming current when it is not suppose to. This type of test requires attaching an ammeter between the battery and your vehicle to determine how much current is being produced by the vehicle's electrical system when the engine isn't on. Be sure to read AEMs wiring instructions before proceeding with the fuel pump and isolating the fuel pump from the factory wiring harness will also be required for sensing, as described in he paragraphs.
In 2019, an incident occurred when Toyota recalled more than 700,000 vehicles for Fuel Pump in which crashes may occur due to possible stalling and electrical problems mainly affecting the battery. The reason why at the time of this recall we discuss on Fuel Pump problems that can create a domino effect in other systems: here link to An Electric Operating Cable issue.
Another means a bad Fuel Pump can impact the battery is with endless cranking before it finally starts. In the event that the Fuel Pump is failing, it may be not supplying fuel properly which causes prolonged cranking times leading to extra demand on your battery. All that pressure over time shortens the life span of the entire battery, hence Gerald's new issue with his dead battery.
As classic automotive engineer Carroll Shelby would have claimed, “A car is only as good as the sum of its parts. If there is a bad Fuel Pump, other parts of this system will eventually get hurt as well (amazingly the battery can comply), so it becomes necessary to look after everything in order to prevent any potential problems.
If you believe your battery is getting drained by the pump going bad, getting it diagnosed and replaced will keep further electrical damage from occurring and prevent being left stranded with a dead battery.